Deterioration of immune function is a prominent hallmark of aging and is only partially explainable by a loss of naïve and central memory CD4 T cells due to thymic involution. Defects in both the innate and adaptive immune system of the elderly have been described and include changes in immune cell-subsets abundance and relative frequencies, altered hematopoiesis, impairments in antigen presentation, decreased B cell as well as T cell proliferation, a reduced TCR repertoire and defect in antibody production (Weiskopf et al., 2009). Ultimately these alterations result in a sharp decline in the response to new and persisting antigens (immunosenescence). Thus it is not surprising that infectious diseases are one of the major causes of mortality in those over the age of 65 and that protective vaccination of the elderly is more difficult to establish than in younger individuals (Goodwin, 2006).
Active immunization and activation of T cell-mediated as well as humoral immune response can be achieved through the administration of immunogenic material or vaccines. Vaccination seeks to prevent, ameliorate or even treat against the harmful effects of pathogens and carcinogens, and regular vaccination has become an integral part of preventive medicine.
Due to the complexity of the immune system, studies of immunosenescence often only investigate one or a few variables of an individual's immune system. This has made it difficult to draw general conclusions about the phenomena being described or how they might relate to each other. Individuals who suffer from an impaired immune function generally face the risk of increased morbidity and mortality. This is particularly relevant for older individuals who show a reduced response to vaccination or have persistent cytomegalovirus infection (Strindhall et al., 2007). The immune system of those individuals can be phenotypically characterized as having an inverted CD4+ to CD8+ T-cell ratio (below one), and a high frequency of CD8+CD28− T-cells (Wikby et al., 2008). There is also evidence that other major causes of mortality in older individuals, such as cardiovascular diseases, cancer and Alzheimer's disease, might involve defects in normal immune function (Hansson, 2005; de Visser et al., 2006; Rojo et al., 2008). This raises the possibility that a functional immune response is a key factor in the maintenance of good health and longevity.
One of the most challenging topics facing the maintenance of good health and longevity is the identification of immunocompromised individuals who might appear healthy, but who have an underlying, undetected impairment of immune function and, so, face the risk of increased morbidity and mortality. The present invention addresses this issue.